1. Field of the Invention
The present invention relates to an imaging method and apparatus for performing multi-planar illumination of a subject, such as parts or organs of the human body. Specifically, the present invention relates to a bi-planar X-ray system capable of simultaneously depicting details of the subject from two different (e.g., orthogonal) perspectives with a reduced amount of exposure to X-ray radiation.
2. Description of the Related Art
Conventionally, biplanar transillumination X-ray systems have been used to create two, quasi-simultaneous images of physiological details of a subject, such as parts or organs of the human body, from two different perspectives. Such images are useful for identifying the location and orientation of bones, organs, arteries and the like and provide significant information which can be used to safely perform critical interventional operations. Further, a sequence of biplanar X-ray images taken over time can be used to visualize, from two perspectives, the progression of an X-ray sensitive dye through arteries or organs in order to monitor the perfusion of blood or medication or to determine the location of blockages therein.
An example of a conventional biplanar X-ray imaging system is disclosed in U.S. Pat. No. 3,440,422 to Ball et al., incorporated herein by reference in its entirety. The system disclosed by Ball et al. includes a first X-ray tube that emits X-ray pulses which travel through a subject and are amplified by an image amplifier tube. The image amplifier tube projects amplified pulse signals onto a photographic film, thereby exposing the film. The first X-ray tube, amplifier and film are oriented relative to the subject, such that an anterior-posterior (AP) two-dimensional image of the subject is formed on a frame of the film for each pulse. The film is advanced with successive pulses, such that a sequence of pulses forms a series of film frames which constitute a moving picture. A second X-ray tube emits X-ray pulses which travel through the subject in a direction substantially orthogonal to the direction of the pulses of the first X-ray tube. The pulses from the second X-ray tube are amplified by a corresponding amplifier tube, and the amplified pulse signals are projected onto a second film to form lateral two-dimensional images of the subject. Thus, moving pictures of the frontal and side views of the subject are respectively formed on the first and second films.
According to the system disclosed by Ball et al., the pulse repetition rate and the pulse duration of the pulses emitted from the first and second X-ray emitters can be adjusted by selecting a frame rate and an exposure time from a selector panel. Importantly, however, pulses must be alternately emitted from the first and second X-ray tubes, and the pulse repetition rate and pulse duration of the pulses from the first and second X-ray tubes cannot differ (i.e., the pulse repetition rates and pulse durations of the two X-ray tubes cannot be adjusted independently). Specifically, the system is capable of generating only alternating pulses, since both X-ray tubes are triggered from different phases of the same oscillating signal.
Similarly, the system disclosed in German Examined Appl. No. 25 23 886 B2 to Stohr provides for an adjustable pulse repetition rate with improved synchronization during rate changes, but does not permit different pulse repetition rates. Like the system disclosed in Ball et al., the first and second X-ray emitters disclosed by Stohr always alternately emit pulses; thus, the pulse repetition rates of the two X-ray emitters cannot differ and cannot be set independently. A timing diagram illustrating the sequence of pulses emitted from the first (waveform A) and second (waveform B) X-ray tubes of such conventional systems is shown in FIG. 1.